1. Field of the Invention
This invention relates to an antenna radio apparatus that is unitarily formed with a wrist band for placement on a person's wrist. In particular, this invention relates to an antenna radio apparatus capable of obtaining a stable operation of an antenna without being affected by different sizes of wrist bands, depending on the persons wearing them, and by a durability of a metal fitting used in the belt-joint of the wrist bands.
2. Related Background Art
FIG. 24 is an example of a miniature portable transmitter/receiver and, more particularly, of an antenna apparatus for a wrist type portable transceiver that is worn on a person's wrist. In FIG. 24, a wrist type transceiver 90 is comprised of a casing 92 (transceiver main body) that incorporates a transceiver circuit board, and a wrist type band 91 providing a first band 91a and a second band 91b having insulating characteristics, which are connected to both sides of the casing 92. A first strip shaped conductive plate 93a and a second strip shaped conductive plate 93b are fixed inside first band 91a and second band 91b, respectively. The first conductive plate 93a and the second conductive plate 93b are electrically connected to the transceiver circuit incorporated in the casing 92 at one of their ends. At their free end side, they are electrically connected to a metal belt-joint (hereinafter called "clasp") 91c and 91d (a fitting of the belt joint) for the first band 91a and the second band 91b.
Therefore, as shown in FIG. 24, when these bands 91a and 91b are connected to each other through clasps 91c and 91d, referring to their equivalent circuit shown in FIG. 25, a first conductive plate 93a and a second conductive plate 93b form a single looped antenna, namely an antenna unit 95, through a transceiver circuit 94 incorporated in a casing 92 and clasps 91c and 91d. Further, the side of the first conductive plate 93a is electrically coupled to a transceiver circuit 94 having a high frequency amplifier circuit 94b, a capacitor 94a and a variable capacitance capacitor 94c attached between a ground potential. The side of the second conductive plate 93b is fixed to the ground potential.
However a conventional antenna 95 for wrist type transceivers has problems in that the peripheral length of the loop varies, causing the inductance value of the antenna to vary, reducing an antenna gain. This occurs because band sizes are different depending on the persons who wear the transceiver. Accordingly, in this case, a problem arises in that a tuning frequency of the antenna 95, expressed by the following formula, is shifted, and an antenna gain is lowered. EQU f=1/[2.pi., (LC).sup.1/2 ]
f: Tuning Frequency PA1 L: Inductance of Antenna PA1 C: Capacitance PA1 .lambda.': Wavelength in Dielectric PA1 .lambda.: Wavelength in Air PA1 .epsilon.: Dielectric Constant of Dielectric
The increased number of times a wrist type band 91 is placed on and off the person's wrist correspondingly gradually raises a contact resistance value of a contact portion due to a deterioration of the shape and surface condition of the conductive clasps 91c and 91d. This disadvantageously results in a larger resistance loss of the antenna 95 together with a degradation of the antenna gain.
Therefore, in order to improve its structure, it is necessary to realize an antenna apparatus for transceivers capable of obtaining a stable operation of an antenna without being affected by different sized wrist bands, depending on the persons who wear them, and by a durability of a metal fitting of the clasp.